Fluid-mechanical suspension system

ABSTRACT

A fluid-mechanical suspension system for a multi-wheeled vehicle providing for each individual wheel to be capable of upward deflection over an obstacle without imparting a similar motion to the vehicle as a whole. Each wheel of the vehicle is carried by a support arm pivotally mounted on the vehicle by way of a spindle journalled in an appropriate bearing to permit a defined amount of vertical displacement of the wheel with respect to the vehicle. A fluid cylinder having a reciprocable piston is actuated by a connecting rod pivotably connected to a crank arm projecting radially from the support arm spindle, such that the volume of the fluid in the cylinder is decreased by an upward vertical displacement of the wheel with respect to the vehicle and increased by a downward vertical displacement of the wheel. Each fluid cylinder is connected to a common source of system pressure, such as a control accumulator, such that each fluid cylinder and its associated mechanical transmission provides a positive rate of change in the vertical force with a corresponding change in wheel displacement. The support arm and the crank arm are angularly mounted on the spindle relatively to each other and to the horizontal, and their effective lengths are such that they form a non-linear variable ratio mechanical transmission or coupling means between the road wheel and the fluid cylinder. A second embodiment of the present invention is disclosed as employing a rotary displacement mechanism in place of the fluid cylinder. In one example of the present invention the fluid-mechanical suspension system is in the form of a plurality of wheels mounted on both sides of a vehicle with the fluid cylinders associated with each wheel being interconnected with one another and a central common accumulator such that the pressure of the fluid in any one of the cylinders is a function of the volume of fluid in the accumulator. The fluid cylinders associated with the corner wheels of the vehicle are preferably provided with a valving mechanism that is operable upon a predetermined pressure differential between the accumulator and its associated fluid cylinder to limit the rate of fluid communication between the fluid cylinder and the common accumulator providing for a dampening of vertical movements of the corner wheels with respect to the vehicle. Means are provided for selectively controlling the height of the vehicle.

Elite States tet [191 randstadter Aug. 14, 1973 FLUID-MECHANICALSUSPENSION SYSTEM [76] Inventor: Jack M. Brandstadter, 1904 Cresthill,Royal Oak, Mich. 48073 [22] Filed: Apr. 26, 1971 [21] Appl. No.: 137,508

[56] References Cited UNITED STATES PATENTS 7/1967 Gustafsson ISO/9.2 R6/1966 Larsen 180/92 R Primary Examiner-Philip Goodman Attorney-Hanke,Gifford & Patalidis [5 7 ABSTRACT A fluid-mechanical suspension systemfor a multiwheeled vehicle providing for each individual wheel to becapable of upward deflection over an obstacle without imparting asimilar motion to the vehicle as a whole. Each wheel of the vehicle iscarried by a support arm pivotally mounted on the vehicle by way of aspindle journalled in an appropriate bearing to permit a defined amountof vertical displacement of the wheel with respect to the vehicle. Afluid cylinder having a reciprocable piston is actuated by a connectingrod pivotably connected to a crank arm projecting radially from thesupport arm spindle, such that the volume of the fluid in the cylinderis decreased by an upward vertical displacement of the wheel withrespect to the vehicle and increased by a downward vertical displacementof the wheel. Each fluid cylinder is connected to a common source ofsystem pressure, such as a control accumulator, such that each fluidcylinder and its associated mechanical transmission provides a positiverate of change in the vertical force with a corresponding change inwheel displacement. The support arm and the crank arm are angularlymounted on the spindle relatively to each other and to the horizontal,and their effective lengths are such that they form a non-linearvariable ratio mechanical transmission or coupling means between theroad wheel and the fluid cylinder.

A second embodiment of the present invention is disclosed as employing arotary displacement mechanism in place of the fluid cylinder.

In one example of the present invention the fluid-mechanical suspensionsystem is in the form of a plurality of wheels mounted on both sides ofa vehicle with the fluid cylinders associated with each wheel beinginterconnected with one another and a central common accumulator suchthat the pressure of the fluid in any one of the cylinders is a functionof the volume of fluid in the accumulator. The fluid cylindersassociated with the corner wheels of the vehicle are preferably providedwith a valving mechanism that is operable upon a predetermined pressuredifferential between the accumulator and its associated fluid cylinderto limit the rate of fluid communication between the fluid cylinder andthe common accumulator providing for a dampening of vertical movementsof the corner wheels with respect to the vehicle. Means are provided forselectively controlling the height of the vehicle.

19 Claims, 16 Drawing Figures PATENIED MIB 14 W3 SHEEI 1 0f 5 s1" I /9 iINVENTOR JACK M. BRANDSTADTE R PAIENTEDAus 14 ms t 3, 752,499

saw u or 5 INVENTOR JACK M. BRANDSTADTER Pmmenwmlm 3.752.499

SHEET 5 0F 5 FIG-l5 INVENTOR JACK M. BRANDSTADTER I FLUID-MECHANICALSUSPENSION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to a fluid-mechanical suspension systemfor absorbing shocks experienced by the wheels of a moving vehicle and,in particular, the invention relates to a fluid-mechanical suspensionsystem in which the vertical motion of each wheel of the vehicle iscoupled by a non-linear variable ratio mechanical transmission to afluid cylinder, all of which are connected to a common source ofpressure to provide a positive rate of change in the vertical forceimparted to each of the wheels as the vertical displacement of thewheels varies.

2. Description of the Prior Art Heretofore, a variety of suspensionsystems have been employed for mounting wheels to a vehicle such thateach individual wheel may deflect upwardly over an obstacle withoutimparting a similar motion to the vehicle as a whole. Such priorsuspension systems have included mechanical or pneumatic springs inconjunction with a suitable connection between the wheel and thevehicle. Such suspension systems are inherently bulky, require shockabsorbers and complicated pneumatic or hydraulic control circuits, inaddition to other components required to regulate or limit the action ofthe suspension.

The prior art suspension systems have been primarily designed from thestandpoint of providing a smooth ride, greater vehicle stability,adjustment to varying loads, and other functional factors. In order tohave high performance characteristics, including a well dampened systemhaving a high load capacity, such prior art systems are complex, heavyand expensive to design and manufacture. Many vehicles, and inparticular military combat vehicles such as tanks, armored personnelcarriers and the like, have a series of individually mounted road wheelswhich carry endless tracks that require a resilient suspension that mustoperate on a very difficult terrain. Most track-type military vehicleshave heretofore employed a torsion bar type of suspension or ahydro-pneumatic type of suspension independently operable to absorb theshocks transmitted by the wheels to the vehicle. These systems, as wellas other conventional suspension systems, are either complex andexpensive, or have limited performance characteristics.

SUMMARY OF THE INVENTION The present invention provides afluid-mechanical system in which each wheel of a vehicle is carried onthe end of a pivotal support arm which is coupled to a fluiddisplacement mechanism by a non-linear variable The fluid-mechanicalsuspension system of the pres-- ent invention eliminates the need ofmechanical or pneumatic springs at each wheel and thus provides afluid-mechanical suspension system having a minimum of components whichresults in a system of low cost, low weight and high reliability.

It is therefore an object of the present invention to provide afluid-mechanical suspension system which furnishes a positive rate ofchange of the vertical force imparted to the wheels which corresponds tothe change in the vertical displacement of each of the vehicle wheelsand which has a low spring rate and large capacity when supporting thestatic weight of the vehicle.

It is also an object of the present invention to provide afluid-mechanical suspension system having performance characteristicscomparable to or greater than the performance characteristics of themore complex, heavier, and more expensive suspension sytems previouslyused.

It is another object of the present invention to provide afluid-mechanical suspension system in which the inter-flow betweenindividual fluid mechanisms controlling the movement of each wheel andwhich are interconnected with a common source of system pressure is usedto advantage to provide an efficient means for dampening the vehicle, aswell as an efficient means for distribution and dissipation of heatgenerated during operation of the system.

Other objects, advantages, and applications of the present inventionwill become apparent to those skilled in the art of fluid-mechanicalsuspension systems when the accompanying description of an example ofthe best mode contemplated for practicing the invention is read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The description herein makes referenceto the accompanying drawings wherein like reference numerals refer tolike parts throughout the several views, and in which:

FIG. 1 is a side elevational view of a military tracked vehicleincorporating a fluid-mechanical suspension system constructed inaccordance with the present invention;

FIG. 2 is a schematic illustration of the fluidmechanical suspensionsystem of the vehicle of FIG. 1;

FIG. 3 is a graphic illustration of the performance characteristics ofan accumulator used in the fluidmechanical suspension system of FIGS. 1and 2;

FIG. 4 is a graphic illustration of the performance characteristics ofthe fluid-mechanical suspension system shown in FIGS. 1 and 2;

FIG. 5 is a fragmentary cross-sectional view of a portion of anon-linear variable ratio mechanical transmission used in thefluid-mechanical suspension system of FIGS. 1 and 2 and taken along line5-5 of FIG. 1;

FIG. 6 is a longitudinal view of the mechanical transmission coupled toa fluid cylinder with the fluidcylinder portion thereof shown insection;

FIG. 7 is a graphic illustration of the relative positions of theseveral components of a suspension unit of the fluid-mechanicalsuspension system with respect to the vertical displacement of the wheelsupported by such suspension unit;

FIG. 8 is a force diagram of the non-linear variable ratio mechanicaltransmission shown in FIG. 6;

FIG. 8a is a schematic representation of a modification of the inventionproviding a simplification of the force diagram of FIG. 8;

FIG. 9 is a fragmentary sectional view of a fluid cylinder showing amodification of the fluid cylinder illustrated in FIG. 6;

FIGS. 10 and 11 are schematic illustrations of modifications of thefluid suspension system of FIGS. 1 and 2;

FIG. 12 is a schematic representation of another modification of theinvention in which a rotary actuator is employed; and

FIGS. l3, l4 and 15 are force diagrams illustrating the manner in whichthe operating characteristics of the modification shown in FIG. 12 maybe varied.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andparticularly to FIG. 1, there is illustrated an armored military combatvehicle 10 of the track type having an endless track 12 at each side ofthe vehicle carried by a drive sprocket 14 at the rearward end of thevehicle and an idler 16 at the forward end of the vehicle. The vehicle10 is supported by a series of individually mounted corner road wheels18 and intermediate road wheels 19 which ride on the track 12 to supportand guide the same. In this example of the invention, four road wheelsare provided at each side of the vehicle, resulting in a total of twoforward and two rear corner wheels 18 and four intermediate road wheels19. However, it is to be understood that the number of road wheels mayvary in accordance with the requirements of particular vehicle design.

As can best be seen in FIGS. 5 and 6, each road wheel 18 or 19 isrotatably fastened to a spindle 20 in a conventional manner, the spindle20, in turn, being fixedly attached to one end of a support arm 22. Thesupport arm 22 is fixedly attached to a second spindle 24 which isjournalled in a bearing 26 carried by the vehicle 10. The opposite endof the spindle 24 projects from the bearing 26 and has a crank arm 28extending radially therefrom which, in turn, is pivotably connected toan end of a connecting rod 30 by any suitable means, such as by the pinand bushing assembly 32 illustrated in FIG. 6. The other end of theconnecting rod 30 is pivotably connected to a piston 34 by any suitablemeans, such as a pin and bushing assembly 39, the piston 34 beingslidably disposed in a cylinder 36 (FIG. 6) or 38 (FIG. 9). The wheelsupport arm 22, the spindle 24 with its bearing 26, the crank arm 28 andthe connecting rod 30 form a non-linear variable ratio mechanicaltransmission or coupling means 35, the operation of which will beexplained in greater detail hereinafter, between the road wheel 18 or 19and the piston 34. 7

Referring to FIG. 2, there is schematically illustrated a fluid circuit40 of the fluid-mechanical suspension system particularly adapted foruse with a vehicle of the type illustrated at FIG. 1. The fluid circuit40 comprises a plurality of fluid cylinders 36 and 38 individuallymounted to the vehicle frame and interconnected by a large capacityfluid conduit 44 to one another and to a fluid accumulator 46. Thecircuit 40 includes a pres sure gage 48 and a fill valve 50, andappropriate connectors for allowing the fluid-mechanical suspensionsystem to be filled initially with an appropriate volume of fluid suchas a hydraulic or transmission fluid and to be replenished as required.The fluid-mechanical suspension system is illustrated as comprising twoforward and two rear comer road wheel supporting fluid cylinders 36 andassociated mechanical transmissions which are adapted to support theforward and rear corner wheels 18 of the vehicle 10 (FIG. 1) and fourintermediate wheel supporting cylinders 38 and associated mechanicaltransmissions which are; adapted to support the intermediate road wheels19.

Referring to FIGS. 6 and 7, there is shown respectively a sectional viewof one of the corner road wheel supporting cylinders 36 with itsassociated mechanical transmission 35, and a graphic representation ofthe mechanical transmission 35 showing the relative position of thecylinder piston 34 as a function of the vertical displacement of a roadwheel 18. Each of s the corner road wheel supporting cylinders 36 isillustrated as comprising a tubular housing 52, having a cylindricalbore 54 in which the reciprocable piston 34 is mounted for relativesliding movement in a conventional manner. A portion of the outerperiphery of the tubular housing 52 has a threaded surface 56 on which acupshaped cap 58 is securely fastened. The cap 58 has a central opening60 through which the connecting rod 30 extends. As viewed in FIG. 6, thecap 58 acts as a stop to limit the rightward movement of the piston 34by engagement with the bottom annular surface 59 of the skirt of thepiston 34.

A valve housing 62 is fastened to the left end of the tubular housing 52by means of a threaded cap 64 which engages the outer threaded periphery66 of the valve housing 62. Seals 68 and 70 respectively carried by thevalve housing 62 and the piston 34 insure a fluid tight seal for apressure chamber 72 formed between the valve housing 62 and the top face74 of the piston 34. The valve housing 62 has a single port 75 toprovide fluid communication between the fluid cylinder 36, via the valvehousing 62, and the accumulator 46 (FIG. 2) through the fluid conduit44. I

The valve housing 62 has two partitions 76 and 78 respectively havingapertures 77 and 79 which, for purpose of description, respectively formthe outlet and inlet of the pressure chamber 72 in the cylinder 36. Theinlet aperture 79 communicates with the pressure chamber 72 through apassageway 80 extending through the partition 76, while the outletaperture 77 is in direct communication with the pressure chamber 72. Thevalve housing 62 includes a pair of area differential valves 82 and 84which are slidably mounted on guide posts 86 and 87 to open and closecommunication between the cylinder pressure chamber 72 and the inlet andoutlet apertures 79 and 77 respectively. Springs 88 and 89 respectivelyassociated with the area differential valves 82 and 84 bias the valvesto the closed position illustrated in FIG. 6.

The valves 82 and 84 require a predetermined pressure differentialacross them prior to opening. The inlet valve 84 is normally biased to aclosed position preventing fluid communication between the fluid conduit44 and the cylinder pressure chamber 72. The accum ulator 46 (FIG. 2)maintains the pressure within the fluid circuit 40 at some selectedpressure which acts against the face of the valve 84, tending to urgethe valve 84 to open communication between the conduit 44 and thepressure chamber 72. At the same time, pressure acting against thepressure chamber side of the piston 84, in addition to the force exertedthereon by the spring 89, tends to maintain the area differential valve84 in a closed position. As the piston 34 is moved rightwardly as viewedin FIG. 6, the pressure on the pressure chamber side of the inlet valve84 will decrease and at some predetermined pressure differential, thevalve 84 will open communication between the conduit 44 and the pressurechamber 72.

The outlet valve 82 operates in a manner similar to the operation of thevalve 84. When the piston 34 is moving in a leftwardly direction asviewed in FIG. 6, the fluid pressure in the cylinder pressure chamber 72will rise, generating force acting against the valve 82 tending to opencommunication between the cylinder pressure chamber 72 and the conduit44. The combined forces exerted by the spring 88 and the system pressureagainst the valve 82 will resist opening of the valve 82 until apredetermined pressure differential exists, at which time the valve 82will open and fluid will be exhausted from the cylinder pressure chamber72. The valves 82 and 84 provide a means for dampening the movement ofthe piston 34 as the same is reciprocated back and forth within thecylinder housing 52. The movement of the piston 34 is a function of thevertical displacement of the wheels 18, all of which will be describedin greater detail hereinafter.

The intermediate cylinders 38 are substantially identical to the cornercylinders 36 with the exception that they are provided with an end cover90 in lieu of the valve housing 62 associated with the corner cylinders38. The fluid pressure chambers 72 in the cylinders 38 are in directcommunication with the conduit 44 through an internally bored passageway91 and port 75, as illustrated in the fragmentary sectional view of FIG.9. The intermediate cylinders 38 may be dampened in a manner similar tothe corner cylinders 36 in applications when desired or required. Intracked vehicles, it is not generally desirable to provide dampening ofthe movement of the intermediate wheels, thus a direct communicationbetween the pressure chambers 72 of each cylinder 38 and the accumulator46 may be provided. However, it is preferable to dampen the movement ofthe corner wheels.

Referring to FIG. 5, and more particularly to FIGS. 6, 7 and 8, it canbe seen that as the vehicle is driven over uneven terrain causing acorner road wheel 18 to be displaced vertically upwardly from a normalposition, or static position, wherein the suspension system supports thestatic weight of the'vehicle, the wheel support arm 22 pivots about theaxis of the spindle 24. Since the support arm 22, the spindle 24 and thecrank arm 28 are fixedly attached to each other, both the support arm 22and the crank arm 28 rotate about the axis of the spindle 24 an equalangular distance. As the crank arm 28 rotates counter-clockwise asviewed in FIG. 6 under the force of the wheel 18 being displaced in anupwardly direction from the static position, the connecting rod 30drives the piston 34 leftwardly, thus resulting in a decrease of thevolume of the pressure chamber 72 within the associated cylinder 36.When the corner wheel 18 is on the contrary vertically lowwhether one ofthe intermediate road wheels 19 is vertically raised or lowered.

It is obvious that when the volume of any of the cylinder pressurechambers 72 is increased as a result of a downward vertical displacementof the corresponding road wheel, fluid is introduced into the cylinderpressure chamber 72 through the common conduit 44 (FIG. 2) from theaccumulator 96, while when the volume of the pressure chamber 72 isdecreased as a result of an upward motion of the corresponding roadwheel, fluid is exhausted from the pressure chamber 72 into the commonconduit 44 to the accumulator 46. The instantaneous fluid pressure inthe system is thus dependent upon the vertical displacement of eachindividual. wheel and the number of wheels thus displaced, upwardvertical displacement of the wheels resulting in an increase of thesystem pressure, while downward vertical displacement of the wheelsresults in an overall decrease of the system pressure. The flow of fluidinto and from the pressure chamber 72 of each cylinder 39 associatedwith the intermediate road wheel is effected substantially unimpeded,while the fluid flow from and into the pressure chamber 72 of each ofthe corner wheel carrying cylinders 36 is not permitted until apredetermined pressure differential is established across the valves 82and 84 as heretofore described, such that the movement of the piston 34within the cylinders 36 and the vertical movement of the corner wheels18 operatively coupled thereto are dampened.

FIG. 6 shows the piston 34 in its leftmost position corresponding to thepoint A in FIG. 7, with the wheel 18 displaced vertically from itsstatic position 8 to an extreme position. The positions of the end ofthe crank arm 28 and of the end of the support arm 22 supporting theroad wheel are graphically indicated in FIG. 7 by points A" and Arespectively. Points A through G in FIG. 7 therefore illustrate thesuccessive positions of the piston 34 as the road wheel 18 is verticallydisplaced to the corresponding positions graphically indicated by pointsA through G, while the points A" through G illustrate the correspondingpositions of the end of the crank arm 28.

The following table is exemplary of a hydromechanical suspension systemaccording to the invention adapted to support a vehicle having a sprungweight of 16,800 lbs. by means of eight road wheels, each of which isadapted to support 2100 lbs. in a static position, reference being hadto FIG. 7:

Vertical position (inches) of the wheel from a static Vertical force F,

Stroke (inches) (Lbs.) imparted position S (FIG. 7) of the piston 34 tothe wheel A 14 A 3.64 3925 B ll B 3.33 3462 C=9 C'=3.07 3170 D 7 D 2.8l2935 E 4 E 2.37 2595- S=0 S'=l.67 2100 F=3 F'= L05 I633 G 5 G 0.04 .978

stantially linear variation in the force F, as the vertical displacementof the wheel changes from static to full displacement.

With reference to FIG. 8 the vertical force F, imparted by the ground ona wheel may be calculated from the following equations:

F a P, A,

wherein F force acting on the piston 34, P, system pressure, and A areaof the piston face.

The reactive force F 1 along the center line of the connecting rod 30 isgiven by the equation:

F, F cos B wherein B angle between the longitudinal center lines of thepiston 34 and of the connecting rod 30.

The torque T at the support arm spindle 24 is given by the equation:

T F1 R2 Sin wherein R radius of the crank arm 28, and C angle betweenthe crank arm 28 and a line perpendicular to the connecting rod whichpasses through the center of rotation of the support arm spindle 24. Thevertical force F, imparted to a wheel is:

and by replacing in equation (5) F by its value as expressed in equation(2):

F, (F, (cos B) R; sin C)/(R, cos A) By substituting F, for its valuefrom equation (1), the expression becomes:

F, (P, A, (cos B) R sin C)/(R cos A) or F, =(P, A, R /R (cos 8 sinC)/cos A Since A,,, R, and R are constant, the change in the verticalforce F, will be a function of the system pressure P, and the relativeangular positions of the connecting rod 30, the crank arm 22 and thesupport arm 32. As the vertical displacement of the wheels increases,even if it is assumed that the system pressure P. remains substantiallyconstant, (cos 8 sin C cos A) increases in a non-linear manner. Thus,the fluidmechanical suspension system of the invention by providing ateach wheel a non-linear variable ratio me chanical transmission couplingbetween the wheel and the fluid cylinder 36 (or 38) results incombination with the common source of system pressure in a positive rateof change of the vertical force imparted to each wheel corresponding toa linear change in the vertical displacement of each wheel.

An alternate structure to the one described and illustrated isschematically represented at FIG. 8a. In such alternate structure, thepiston 34 in the cylinder 36 (or 38) is provided with a rigid connectingrod 30' having its end pivotally connected to the end of the crank arm28. The cylinder 36 (or 38) is pivotally mounted relative to the vehiclehull, such as by means of a mounting flange 37 provided with a pivotalattachment means shown at 39, to permit the center line of the cylinderto be at all time aligned with the center line of the connecting rod30'. With such a structure, equation (8) becomes:

F, (P, A, R /R,) (sin C/cos A) The non-linear variable ratio mechanicaltransmission 35 causes positive suspension of the vehicle under allconditions. in other words, if the center of gravity of the vehicle isshifted, for example, to one side of its center line, all the wheels onthe side of the vehicle corresponding to the side to which the center ofgravity has been shifted are caused to support a greater load, while allthe wheels on the other side are caused to support a comparativelydecreased load. Because the vertical F imparted by a wheel on the groundis always positive, as a result of each term of equation (8) or equation(9) being always positive, the vehicle is constantly supported by thesuspension system of the invention. By comparison, if the mechanicalcoupling between the wheel support arm and the fluid cylinder piston wasa linear constant ratio mechanical transmission, tilting of the vehicleas a result of a shift of its center of gravity to one side of itscenter line would result in exhausting fluid from the fluid cylinders onthe lower side and introducing fluid into the fluid cylinders on thehigher side of the vehicle. Such a suspension system, with a linearconstant ratio mechanical transmission, would be incapable of operatingas a vehicle fluid suspension system, unless each individual suspensionfluid cylinder is provided with its own individual accumulator, as eachpiston would be capable only of displacing fluid through the common lineinto the other cylinders to cause proportional displacement of thepiston in such other cylinders, without any of the self-equilibrationeffect generally associated with a suspension system. In effect, the useof a linear constant ratio mechanical coupling between the road wheelsof a vehicle and their associated suspension fluid cylinders, instead ofthe non-linear variable ratio mechanical coupling of the inv a A?Consequently, the reactive force F on the ground is substantiallyconstant as the system pressure P, is substantially constant. Theequilibrium self-seeking capability of such a system is thereforesubstantially nonexistent.

Another alternate structure to the one described and illustrated inFIGS. 1-8 is schematically represented in FIG. 12. In this alternatestructure the fluid cylinders 36 and 38 are replaced by a rotarydisplacement mechanism 104 comprising a housing 106 rigidly fastened tothe vehicle structure and an angularly displacable rotor 108 providedwith vanes 109 dividing the interior of the housing into pressurechambers 111 and 113. An arm 1 10 having a length R as measured alongits longitudinal centerline from the axis of rotation of the rotor 108is attached to the end of a rotor shaft (unnumbered) projecting from thehousing 106. The arm 110 radially extends from the rotor shaft forconnecting to the crank arm 28 of the spindle assembly by means of anappropriate connecting rod 112, the opposite ends of which are pivotallyconnected to the ends of the arm 110 and the crank arm 128 by pin andbushing assemblies 114 and 32, respectively, in a manner similar to thataforementioned with respect to the arrangments disclosed in FIGS. l9.The rotary mechanism 104, which is similar in construction to aconventional rotary actuator, has fluid inlet ports 116 and 118connecting the pressure chambers 111 to line 44 which, in turn, isconnected to a source of fluid pressure with the remaining of the systembeing as hereinbefore described. The pressurized fluid introducedthrough inlet ports 116 and 118 into the pressure chambers 1 11 on oneside of the vanes 109 urge the rotor 108 in a clockwise direction, asviewed in FIG. 12, to oppose the upward vertical force applied by thewheel 18 mounted at the end of support arm 22. The chambers 113 withinthe housing 108 are normally vented to atmosphere. The crankarm 28,spindle 24, the wheel support 22 and the wheel 18 carried thereby areidentical to the structure described hereinbefore and thus a furtherdescription thereof is not necessary.

With reference to FIG. 13, the vertical force F,, imparted by the groundonto the wheel may be calculated from the following equation:

a a en/ F TAR, sin D) wherein D acute angle between the center line ofthe connecting rod 112 and the center line of the arm 110.

The torque T at the support arm spindle 24 is given by the equation:

T= F 1;: sin c wherein R the radius of the crank arm 28 and C= the anglebetween the crank arm and a line perpendicular to the connecting rodI12which passes through the center of rotation of the support arm spindle24. The vertical force F imparted to the wheel is:

F,, I/(R cos A) wherein R, the radius of the support arm 22 and A anglebetween the support arm 22 and the hori zontal. By replacing in equation(14) the torque T by its value as expressed in equation (13),

v R sin C)/(R cos A) and by replacing in equation (15) F by its value asexpressed in equation (l2), and by substituting F,, for its value fromequation (11), the expression becomes:

F,, (T R 'sin C)/(R sin D-R cos A) F,, (P, D /21r) (R /R R (sin C/sin Dcos A) Since D,,, R,, R and R are constant, the change in the verticalforce F is a function of the system pressure P, and the relative angularpositions of the connecting rod 112, the crank arm 28, the support arm22 and the arm 110. Thus, in suspension systems employing the rotarymechanism 104, the charactieristic of the force F versus displacement ofthe wheel 18 may be additionally varied by changing the initial angularposition of the am 110.

FIGS. 13, 14 and 15 illustrate three variations in the initial angularposition of the arm to provide for selected variations in the force Fand thus the vertical 5- pring rate of the wheels 18.

In FIG. 13 the arm 110 of the rotor 108 is illustrated as being locatedat when the wheel 18 is at its lowest vertical position; at 122 when thewheel 18 is in an intermediate position; and at 124 when the wheel 18 isdisplaced upwardly to a maximum vertical position. Since F is relativelyconstant along this range of angular movement of the arm 110, thevehicle spring rate is similar to that of the linear mechanism describedheretofore in the description of the embodiments disclosed in FIGS. 1-8and 8a.

In FIG. 14 the positions of the arm 1 10 between maximum and minimumdisplacement of the wheel 18 are shown as varying to the left of thevertical. In this configuration the force F, increases as the wheel 18moves upwardly. That is, as the arm 110 is rotated counterclockwise thespring rate of the wheel increases as the wheel moves upwardly.

In FIG. 15 the initial position of the arm 1 10 is to the right of thevertical, that is, angularly displaced in a clockwise direction asviewed in FIG. 15. In this embodiment the force F, decreases during theinitial upward movement of the wheel 18 and then remains relativelyconstant as in the configuration shown in FIG. 13. Thus a lower springrate is provided at and around the static height of the vehicle with anincrease therein to a relatively constant spring rate as the wheels 18move upwardly.

FIG. 3 illustrates the system pressure characteristics of a typicalaccumulator 46, for example a Greer A- 104-200 accumulator having acapacity of 555 in. as a function of the volume of hydraulic fluidpresent in the accumulator. In the present example, the minimum systempressure is illustrated as being 1560 psi with all road wheels at theposition G of FIG. 7, the pressure in the system when in a staticcondition is 1732 psi with all road wheels at the position S, and themaximum pressure of the system is 3540 psi with all road wheels at theposition A.

FIG. 4 graphically illustrates the vertical force exerted on the roadwheels as a function of the vertical displacement of the wheels. Curve aillustrates the performance characteristics of one wheel at 1732 psisystem static pressure. Curve b illustrates the performancecharacteristics of two wheels at an initial system static pressure of1732 psi. Curve c illustrates the performance characteristics of thesystem when all eight wheels are vertically displaced. Curve dillustrates the dampening force of the corner wheels when a differentialpressure of 1000 psi is utilized for opening the differential area valve82 (FIG. 6). FIG. 4 clearly shows that the fluid-mechanical suspensionsystem of the present invention having a non-linear variable ratiomechanical transmission coupling each road wheel support arm to a fluidcylinder, in combination with a common pressure source, has a positiverate of change of the force exerted by the road wheels on the ground,resulting from a positive wheel displacement. It can also be seen thatthe spring rate of the suspension system and the energy storage capacityof the system increase with an increase in both the number of wheelsdisplaced and the amount of vertical displacement of each wheel. This isdue to the interconnection of the fluid cylinders of the system by wayof a large capacity conduit 44 (FIG. 2) such that a high flow rate isestablished between the cylinders and the accumulator with a minimum ofline loss. By interconnecting the several fluid cylinders with oneanother and with the accumulator, and by providing the non-linearvariable ratio mechanical transmission of the invention as a couplingmeans between the wheel suspension arms and their associated fluidcylinders, the need for auxiliary mechanical or pneumatic springs in thesuspension is completely eliminated, thus reducing the total weight ofthe suspension system to a minimum. For example, in the describedembodiment of the invention, the total weight of the fluid-mechanicalsuspension system required to provide a suspension for a 16,800 lbs.vehicle is less than 300 lbs., not including the total weight ofelements such as the suspension arms, road wheels and the like which arecommon to any suspension system. At the same time, the use of a minimumnumber of simple, lightweight parts insures a low cost system. Byproviding the non-linear variable ratio mechanical transmission of theinvention using an appropriate geometrical relationship between theconnecting rod, the crank arm and the wheel support arm, up to 105 ofwheel support arm rotation, as shown at FIGS. 6 and 7, can beaccommodated by the suspension system.

Since it is not necessary to store energy at each of the individualwheels to support the static weight of the vehicle, a low spring rateand long stroke for each wheel is attainable, as clearly shown by theforcedisplacement curves a, b and c of FIG. 4.

The,flow of fluid between the fluid cylinders and the accumulatorprovides an efflcient means for dampening the vehicle, as well as ameans for distributing and dissipating the heat generated at each of thefluid cylinders during the operation of the suspension system. Thisability of the system to dissipate and store energy as a function of thelong stroke of the fluid cylinders combined with the dampening andaccumulator capacity is sufficient to decelerate the downward velocityof a vehicle which has been thrown into the air, such as by hitting alarge obstacle in the road at high speed, without the road arms strikingvertical displacement stops which are normally provided on suchvehicles.

Since a minimum number of simple and rugged parts are used in thesuspension system, only one dynamic seal per actuation is required, thereliability of the system is substantially increased over the prior artdesigns. Since the substantially same structure is used and thestructures for the comer wheel and intermediate wheel cylinders, of allthe wheel support arms, all the crank arms, and all the journals andbearings are identical, the cost of manufacturing and maintaining thesystem is at a minimum due to the interchangeability of thesecomponents.

Referring now to FIGS. 10 and 11, there is schematically illustratedtherein an additional feature of the invention for controlling thestatic height of the vehicle. By varying the static pressure of thesystem, the position of the piston or vanes may be varied in eachcylinder and thus the vertical height of the wheels may be varied overtheir full range of vertical displacement. Thus, by having a low systemstatic pressure, the vehicle may be lowered with respect to the groundon which it is carried. By increasing the system static pressure, thevehicle may be raised to any desired position or an optimum height maybe maintained with changes in vehicle gross weight.

FIG. 10 illustrates a manual control mechanism for varying the systempressure which comprises a reservoir of fluid 91, a hand pmp 92 havingits inlet connected to the reservoir and its outlet connected to theconduit 44, and a return valve 93 connected between the conduit 44 andthe reservoir 91. The manual control mechanism allows the operator ofthe vehcle to manually pressurize the system by means of the pump 92 toraise the vehicle to any desired vertical height, and by opening thereturn valve 93 to lower the vehicle.

FIG. 11 illustrates a power control mechanism 94 for varying the systempressure which comprises a reservoir of fluid 95, a motor driven pump 96for transferring fluid from the reservoir to the conduit 44, a solenoidoperated valve 98 disposed between the conduit 44 and the reservoir anda control switch 100 for selectively actuatingthe solenoid operatedvalve 98 or the motor driven pump 96, whereby the operator may vary theheight of the vehicle to a lower or higher position rapidly andeffortlessly by utilizing the vehicle electrical power supply. Thesystem pressure is raised and the vehicle raised to a higher staticposition when the pump 96 is actuated, while the system pressure islowered and the vehicle lowered to a lower static position when thereturn valve 98 is open. The control switch 100, illustrated in FIG. 11,may be replaced by a variable setting pressure switch which enables thesystem to automatically maintain a pre-set pressure causing a resultantvehicle height despite changes in the fluid volume due to ambient andsystem temperature variation and losses of fluid due to seal leakage.

in addition, if so desired, a manual or solenoid operated valve(indicated schematically in FIG. 2 by the numeral 102) may be attachedto each individual cylinder 36 and/or 38 for selectively closing offfluid communication between the pressure chamber 72 and the conduit 44,thereby trapping fluid within the pressure chamber 72 (FIG. 6) to lockout the suspension system pressure from that particular cylinder andmaintain the wheel carried thereby at a specific position.

It can thus be seen that the present invention provides afluid-mechanical suspension system which supports a vehicle at a desiredstatic height and which, in conjunction with the mechanisms disclosed,has a nonlinear ratio spring rate having a positive rate of change offorce as the wheels of the vehicle are vertically displaced. Thesuspension system disclosed is rugged, lightweight, of low cost, and hashigh performance characteristics, all of which are not available in theprior art suspension systems.

Although only a few embodiments of the invention have been disclosed, itwill be apparent to those skilled in the art of such fluid-mechanicalsuspension systems that many changes may be had without departing fromthe spirit of the invention or the scope of the appended claims.

What is claimed is as follows:

1. A fluid-mechanical suspension system for mounting a plurality ofwheels to a vehicle, said system comprising means forming a plurality ofexpansible fluid pressure chambers respectively associated with saidplurality of wheels, each of said pressure chambers having;a movablewall member, a plurality of non-linear variable ratio mechanicaltransmissions, each operatively connecting each of said movable wallmembers to the wheel associated therewith, a source'of fluidpressure,and means connecting to said source of fluid pressure each ofsaid pressure chambers cooperating with its associated mechanicaltransmission to provide a positive rate of change in the vertical forceexerted on its associated wheel as a function in the. change in thevertical displacement of said associated wheel, wherein said mechanicaltransmission is operatively connected to said movable wall member of itsassociated fluid chamber in such a manner that vertical movement of saidwheel in one direction causes expansion of said associated chamber,while vertical movement of said wheel in an opposite direction causescontraction of said associated chamber creating a pressure therein thatexerts a force on said movable wall resisting said contraction, anaccumulator means and fluid conducting means interconnecting saidpressure chambers and said accumulator means, whereby the pressure inone of said pressure chambers is a function of the pressure in theothers of said pressure chambers.

2. The fluid-mechanical suspension system of claim 1 wherein each ofsaid means forming an expansible pressure chamber comprises a fluidcylinder and a piston reciprocally mounted within said fluid cylinderand defining therewith said expansible pressure chamber,

said piston being operatively coupled to said associated wheel by saidnon-linear variable ratio mechanical transmission.

3. The fluid mechanical suspension system of claim 1 wherein each ofsaid means forming an expansible pressure chamber comprises a rotaryactuator having a stator with a rotor rotatably mounted therein anddefining said expansible pressure chamber, said rotor being operativelycoupled to said associated wheel by said non-linear variable ratiomechanical transmission.

4. The fluid-mechanical suspension system of claim 1 wherein saidnon-linear variable ratio mechanical. transmission comprises bearingmeans carried by said vehicle, a spindle rotatable in said bearingmeans, a crank arm radially extending from said spindle and rotatabletherewith, a wheel support arm radially extending from said spindle androtatable therewith, said support arm rotatably supporting saidassociated wheel, and rod means for connecting said movable wallmemberto the radially extending end of said crank arm.

5. The fluid-mechanical suspension system of claim 4 wherein each ofsaid means forming an expansible pressure chamber comprises a fluidcylinder and a piston reciprocably mounted within said fluid cylinderand defining therewith said expansible pressure chamber on one side ofsaid piston, the other side of said piston being operatively coupled tosaid rod means.

6. The fluid-mechanical suspension system of claim 5 wherein said rodmeans is a connecting rod rigidly coupled to said piston and wherein thevertical force F exerted on each wheel is determined by the followingformula:

F, (P, A,, R /R (sin C/cos A) wherein P, is the pressure in theassociated fluid cylinder, A, is the area of the piston exposed to fluidin said associated fluid chamber, R is the length of said crank arm, Ris the length of said support arm, C is the angle between the crank armand a line perpendicular to the connecting rod passing through thecenter of rotation of the spindle, and A is the angle between thesupport arm and the horizontal.

7. The fluid-mechanical suspension system of claim 6 wherein saidmechanical transmission is operatively connected to said movable wallmember of its associated fluid cylinder in such a manner that verticalmovement of said wheel in one direction causes expansion of saidassociated chamber, while vertical movement of said wheel in an oppositedirection causes contraction of said associated chamber creating apressure therein that exerts a force on said movable wall resisting saidcontraction, an accumulator means and fluid conducting meansinterconnecting said pressure chambers and said accumulator means,whereby the pressure in one of said pressure chambers is a function ofthe pressure in the other of said pressure chamber, and furthercomprising means for selectively varying the pressure of said fluid.

8. The fluid-mechanical suspension system of claim v5 wherein said rodmeans is a connecting rod pivotably coupled to said piston and whereinthe vertical force F exerted on each wheel is detennined by thefollowing formula:

F, (P, A R IR (cos B sin C/cos A) wherein P, is the pressure in theassociated fluid cylinder, A is the area of the piston exposed to fluidin said associated fluid chamber, R is the length of said crank arm, Ris the length of said support arm, B is the angle between thelongitudinal center lines of the piston and of the connecting rod, C isthe angle between the crank arm and a line perpendicular to theconnecting rod passing through the center of rotation of the spindle andA is the angle between the support arm and the horizontal.

9. The fluid-mechanical suspension system of claim 8 wherein saidmechanical transmission is operatively connected to said movable wallmember of its associated fluid cylinder in such a manner that verticalmovement of said wheel in one direction causes expansion of saidassociated chamber, while vertical movement of said wheel in an oppositedirection causes contraction of said associated chamber creating apressure therein that exerts a force on said movable wall resisting saidcontraction, an accumulator means and fluid conducting meansinterconnecting said pressure chambers and said accumulator means,whereby the pressure in one of said pressure chambers is a function ofthe pressure in the other of said pressure chambers; and furthercomprising means for selectively varying the pressure of said fluid.

10. The fluid mechanical-suspension system of claim 4 wherein each ofsaid means forming an expansible pressure chamber comprise a rotarydisplacement mechanism having a housihg with an angularly displacablepressure responsive piston mounted therein and forming said expansiblepressure chamber, said piston being operatively coupled to said means.

11. The fluid-mechanical suspension system of claim 10 wherein said rodmeans comprises a piston arm carried by said piston and angularlydisplacable therewith and a connecting rod pivotaby coupling said pistonarm the vertical force F, exerted on each wheel is determined by thefollowing formula:

F, (P, D /21r) (R ,R, R (sin C/sin D cos A) wherein P, is pressure inthe rotary displacement mechanism, D is the displacement per revolutionof the rotary dispacement mechanism, R is the length of the suppoRt art,R is the length of the crank arm, R is the length of the piston arm, Ais the angle between the support arm and the horizontal, C is the anglebetween the crank arm and a line perpendicular to the connecting rodwhich line passes through the center of rotation of the spindle, and Dis an acute angle between the center line of the connecting rod and thecenter line of the piston arm.

12. The fluid-mechanical suspension system of claim 11 wherein saidmechanical transmission is operatively connected to said movable wallmember of its associated rotary displacement mechanism in such a mannerthat vertical movement of said wheel in one direction causes expansionof said associated chamber, while vertical movement of said wheel in anopposite direction causes contraction of said associated chambercreating a pressure therein that exerts a force on said movable wallresisting said contraction, an accumulator means and fluid conductingmeans interconnecting said pressure chambers and siad accumulator means,whereby the pressure in one of said pressure chambers in a function ofthe pressure in the other of said pressure chambers; and furthercomprising means for selectively varying the pressure of said fluid.

13. The fluid-mechanical suspension system of claim 1 wherein a selectednumber of said fluid chambers comprise an inlet and an outlet placingsaid pressure chambers in communication with said means connecting saidpressure chamber to said source of fluid pressure, first pressureresponsive valve means cooperating with said inlet for preventing fluidcommuncation between said chamber and said fluid connecting means untilthe pressure in said fluid connecting means exceeds the pressure in saidpressure chamber by a predetermined amount, and second pressureresponsive valve means cooperating with said outlet for preventing fluidcommunication between said pressure chamber and said fluid connectingmeans until the pressure of the fluid in said pressure chamber exceedsthe pressure in said fluid connecting means by a predetermined amount.

14. The fluid-mechanical suspension system of claim 13 wherein each ofsaid pressure responsive valve means further comprises spring meansbiasing said valve means to a position cutting off communication betweensaid pressure chamber and said fluid connecting means.

15. The fluid-mechanical suspension system of claim 13 wherein each ofsaid means forming an expansible pressure chamber comprises a fluidcylinder and a piston reciprocably mounted with said fluid cylinder anddefining therewith said expansible pressure chamber, and said pistonbeing operatively coupled to said associated wheel by said mechanicaltransmission.

16. The fluid-mechanical system as defined in claim 13 wherein each ofsaid means forming an expansible pressure chamber comprises a rotarydisplacement mechanism having a housing with an angularly displacablepressure responsive piston mounted therein and forming said expansiblepressure chamber, said piston being operatively coupled to saidassociated wheel by said mechanical transmission.

17. The fluid-mechanical system of claim 1 further comprising means forselectively preventing communication between said source of fluidpressure and each of said pressure chambers.

18. The fluid-mechanical suspension system of claim 1 further comprisingmeans for selectively varying the pressure of said fluid.

19. The fluid-mechanical suspension system of claim 18 wherein thevertical force exerted on said associated wheel is increased when thepressure of said fluid is increased and the vertical force exerted onsaid wheel is decreased when said pressure is decreased whereby theheight of said vehicle may be selectively varied.

BJA-lO2-A UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3 ,752,49 V Dated August 14, 1973 PatentNo.

Inventor s) JACK BRANDS TADTE R It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

" IN 'rHE SPECIFICATION Column 4, line 16, after "of" delete "s" Column7, correct equation (4) to:

.-' F (R cos A) correct equation I (8) to:

- orfjF (P A R /R (cos B sin C/cos A) Column 9 correct equation (12) to:

i i 3 i D Colurr xn lo correct equation (14) to:

line ll, correct the epelling of "characteristic" Column 12, line 5l,correct the spellingof "vehicle" FORM PO-105O (10-69) uscoMM- Dc 6375P69 1 I w u.s. eovznu'uzu-r warms omcs was o-ssa-au.

tent No. 3,752,499

IN THE CLAIMS column 15, line 31, after "said' insert rod line 35,correct the spelling of "pivotably" line 36, after "arm" insert to saidradially extending end of said crank arm, wherein line 43, correct thespelling of "support arm' Column 16, line 3, correct the spelling of"said" 'Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer I ActingCommissioner of Patents c

1. A fluid-mechanical suspension system for mounting a plurality ofwheels to a vehicle, said system comprising means forming a plurality ofexpansible fluid pressure chambers respectively associated with saidplurality of wheels, each of said pressure chambers having a movablewall member, a plurality of non-linear variable ratio mechanicaltransmissions, each operatively connecting each of said movable wallmembers to the wheel associated therewith, a source of fluid pressure,and means connecting to said source of fluid pressure each of saidpressure chambers cooperating with its associated mechanicaltransmission to provide a positive rate of change in the vertical forceexerted on its associated wheel as a function in the change in thevertical displacement of said associated wheel, wherein said mechanicaltransmission is operatively connected to said movable wall member of itsassociated fluid chamber in such a manner that vertical movement of saidwheel in one direction causes expansion of said associated chamber,while vertical movement of said wheel in an opposite direction causescontraction of said associated chamber creating a pressure therein thatexerts a force on said movable wall resisting said contraction, anaccumulator means and fluid conducting means interconnecting saidpressure chambers and said accumulator means, whereby the pressure inone of said pressure chambers is a function of the pressure in theothers of said pressure chambers.
 2. The fluid-mechanical suspensionsystem of claim 1 wherein each of said means forming an expansiblepressure chamber comprises a fluid cylinder and a piston reciprocallymounted within said fluid cylinder and defining therewith saidexpansible pressure chamber, said piston being operatively coupled tosaid associated wheel by said non-linear variable ratio mechanicaltransmission.
 3. The fluid mechanical suspension system of claim 1wherein each of said means forming an expansible pressure chambercomprises a rotary actuator having a stator with a rotor rotatablymounted therein and defining said expansible pressure chamber, saidrotor being operatively coupled to said associated wheel by saidnon-linear variable ratio mechanical transmission.
 4. Thefluid-mechanical suspension system of claim 1 wherein said non-linearvariable ratio mechanical transmission comprises bearing means carriedby said vehicle, a spindle rotatable in said bearing means, a crank armradially extending from said spindle and rotatable therewith, a wheelsupport arm radially extending from said spindle and rotatabletherewith, said support arm rotatably supporting said associated wheel,and rod means for connecting said movable wall member to the radiallyextending end of said crank arm.
 5. The fluid-mechanical suspensionsystem of claim 4 wherein each of said means forming an expansiblepressure chamber comprises a fluid cylinder and a piston reciprocablymounted within said fluid cylinder and defining therewith saidexpansible pressure chamber on one side of said piston, the other sideof said piston being operatively coupled to said rod means.
 6. Thefluid-mechanical suspension system of claim 5 wherein said rod means isa connecting rod rigidly coupled to said piston and wherein the verticalforce Fv exerted on each wheel is determined by the following formula:Fv (Ps Ap R2/R1) (sin C/cos A) wherein Ps is the pressure in theassociated fluid cylinder, Ap is the area of the piston exposed to fluidin said associated fluid chamber, R2 is the length of said crank arm, R1is the length of said support arm, C is the angle between the crank armand a line perpendicular to the connecting rod passing through thecenter of rotation of the spindle, and A is the angle between thesupport arm and the horizontal.
 7. The fluid-mechanical suspensionsystem of claim 6 wherein said mechanical transmission is operativelyconnected to said movable wall member of its associated fluid cylinderin such a manner that vertical movement of said wheel in one directioncauses expansion of said associated chamber, while vertical movement ofsaid wheel in an opposite direction causes contraction of saidassociated chamber creating a pressure therein that exerts a force onsaid movable wall resisting said contraction, an accumulator means andfluid conducting means interconnecting said pressure chambers and saidaccumulator means, whereby the pressure in one of said pressure chambersis a function of the pressure in the other of said pressure chamber, andfurther comprising means for selectively varying the pressure of saidfluid.
 8. The fluid-mechanical suspension system of claim 5 wherein saidrod means is a connecting rod pivotably coupled to said piston andwherein the vertical force Fv exerted on each wheel is determined by thefollowing formula: Fv (Ps Ap R2/R1) (cos B sin C/cos A) wherein Ps isthe pressure in the associated fluid cylinder, Ap is the area of thepiston exposed to fluid in said associated fluid chamber, R2 is thelength of said crank arm, R1 is the length of said support arm, B is theangle between the longitudinal center lines of the piston and of theconnecting rod, C is the angle between the crank arm and a lineperpendicular to the connecting rod passing through the center ofrotation of the spindle and A is the angle between the support arm andthe horizontal.
 9. The fluid-mechanical suspension system of claim 8wherein said mechanical transmission is operatively connected to saidmovable wall member of its associated fluid cylinder in such a mannerthat vertical movement of said wheel in one direction causes expansionof said associated chamber, while vertical movement of said wheel in anopposite direction causes contraction of said associated chambercreating a pressure therein that exerts a force on said movable wallresisting said contraction, an accumulator means and fluid conductingmeans interconnecting said pressure chambers and said accumulator means,whereby the pressure in one of said pressure chambers is a function ofthe pressure in the other of said pressure chambers; and furthercomprising means for selectively varying the pressure of said fluid. 10.The fluid mechanical-suspension system of claim 4 wherein each of saidmeans forming an expansible pressure chamber comprise a rotarydisplacement mechanism having a housihg with an angularly displacablepressure responsive piston mounted therein and forming said expansiblepressure chamber, said piston being operatively coupled to said means.11. The fluid-mechanical suspension system of claim 10 wherein said rodmeans comprises a piston arm carried by said piston and angularlydisplacable therewith and a connecting rod pivotab y coupling saidpiston arm the vertical force Fv exerted on each wheel is determined bythe following formula: Fv (Ps Da/2 pi ) (R2/R1 R3) (sin C/sin D cos A)wherein Ps is pressure in the rotary displacement mechanism, Da is thedisplacemeNt per revolution of the rotary dispacement mechanism, R1 isthe length of the suppoRt art, R2 is the length of the crank arm, R3 isthe length of the piston arm, A is the angle between the support arm andthe horizontal, C is the angle between the crank arm and a lineperpendicular to the connecting rod which line passes through the centerof rotation of the spindle, and D is an acute angle between the centerline of the connecting rod and the center line of the piston arm. 12.The fluid-mechanical suspension system of claim 11 wherein saidmechanical transmission is operatively connected to said movable wallmember of its associated rotary displacement mechanism in such a mannerthat vertical movement of said wheel in one direction causes expansionof said associated chamber, while vertical movement of said wheel in anopposite direction causes contraction of said associated chambercreating a pressure therein that exerts a force on said movable wallresisting said contraction, an accumulator means and fluid conductingmeans interconnecting said pressure chambers and siad accumulator means,whereby the pressure in one of said pressure chambers in a function ofthe pressure in the other of said pressure chambers; and furthercomprising means for selectively varying the pressure of said fluid. 13.The fluid-mechanical suspension system of claim 1 wherein a selectednumber of said fluid chambers comprise an inlet and an outlet placingsaid pressure chambers in communication with said means connecting saidpressure chamber to said source of fluid pressure, first pressureresponsive valve means cooperating with said inlet for preventing fluidcommuncation between said chamber and said fluid connecting means untilthe pressure in said fluid connecting means exceeds the pressure in saidpressure chamber by a predetermined amount, and second pressureresponsive valve means cooperating with said outlet for preventing fluidcommunication between said pressure chamber and said fluid connectingmeans until the pressure of the fluid in said pressure chamber exceedsthe pressure in said fluid connecting means by a predetermined amount.14. The fluid-mechanical suspension system of claim 13 wherein each ofsaid pressure responsive valve means further comprises spring meansbiasing said valve means to a position cutting off communication betweensaid pressure chamber and said fluid connecting means.
 15. Thefluid-mechanical suspension system of claim 13 wherein each of saidmeans forming an expansible pressure chamber comprises a fluid cylinderand a piston reciprocably mounted with said fluid cylinder and definingtherewith said expansible pressure chamber, and said piston beingoperatively coupled to said associated wheel by said mechanicaltransmission.
 16. The fluid-mechanical system as defined in claim 13wherein each of said means forming an expansible pressure chambercomprises a rotary displacement mechanism having a housing with anangularly displacable pressure responsive piston mounted therein andforming said expansible pressure chamber, said piston being operativelycoupled to said associated wheel by said mechanical transmission. 17.The fluid-mechanical system of claim 1 further comprising means forselectively preventing communication between said source of fluidpressure and each of said pressure chambers.
 18. The fluid-mechanicalsuspension system of claim 1 further comprising means for selectivelyvarying the pressure of said fluid.
 19. The fluid-mechanical suspensionsystem of claim 18 wherein the vertical force exerted on said associatedwheel is increased when the pressure of said fluid is increased and thevertical force exerted on said wheel is decreased when said pressure isdecreased whereby the height of said vehicle may be selectively varied.